1. Field of the Invention
This invention relates to a catalyst support with a unique bidisperse micropore size distribution and to the resulting hydroprocessing catalyst which is made from the support and to a process to hydrotreat heavy petroleum feeds.
2. Description of the Previously Published Art
Shiroto et al in U.S. Pat. No. 4,444,655 discuss extensively eight different types of processes for hydrotreating using various kinds of catalysts and point out that none of the processes is satisfactory. Their solution is to use a catalyst having 1-30% by of catalytic metals (1) where the average pore diameter (APD) is from about 180 to 500 Angstrom units, (2) where the minimum total pore volume is calculated by a formula which is dependent on the APD and which has at least 0.35 cc/g of volume in pores from 180 to about 500 Angstrom units and (3) where the total surface area is at least 104 m.sup.2 /g.
Of interest to the present invention is Shiroto et al's description of processes for hydrodesulfurization and demetallization characterized by using a catalyst having a double peak in its pore volume. This is their prior art process (5) which they say "is based on the fact that in the hydrotreatment of heavy hydrocarbon oils, desulfurization is not very largely influenced by intrapore diffusion, while demetallization is largely affected by it. According to this process, there is used a catalyst provided with both small pores having a diameter not greater than about 100 Angstrom units, and macropores having a diameter of at least about 500 Angstrom units, or even at least about 1,000 Angstrom units. Although this catalyst does certainly relax the limitations relating to the diffusion of metal-containing high molecular compounds into the pores, it shows a sharp reduction in activity due to metal accumulation in the pores having a diameter not greater than about 100 Angstrom units, and the mouths of these pores are likely to be blocked, as is the case with the catalyst used for the group (1) [which is their prior art catalyst with small pores]. Thus, the catalyst for the group (5) fails to maintain a high activity for a long time for the feedstock oil having a high metal content, and eventually, only the larger pores act mainly for demetallization. Therefore, it is not considered to have an improved efficiency over the catalysts for groups (1) and (3) [which is their prior art catalyst with macro pores] which are used individually."
Mulaskey in U.S. Pat. No. 4,102,822 discloses a catalyst composition in the form of a pack of particles with different size particles without reference to the pore size distribution of these particles. There are channels forming interconnected macropores which contribute from 3 to 45 of the pore volume. A further and special advantage of the catalyst is that a mixture of two or more different kinds of particles having different catalytic activities may be used in the preparation of the catalyst pack or cluster therein, thereby yielding a catalyst having bi- or polymodal activity.